The present disclosure relates to a fixing device configured to fix a toner image on a recording medium and an image forming apparatus provided with the fixing device.
An electrographic image forming apparatus such as a printer or a copying machine forms a toner image on a surface of a recording medium such as a sheet, and subsequently, heats and pressures the recording medium and the toner image by a fixing device, thereby fixing the toner image on the recording medium.
As a manner of the above-mentioned fixing device, a manner of forming a fixing nip for heating and pressuring a recording medium and a toner image by a fixing roller and a pressuring roller is known. The above-mentioned fixing roller is formed by covering an outer circumferential face of a metallic cored bar with a resin having a high toner release property, for example. Also, as a heat source for heating the above-mentioned fixing roller, a halogen heater is used, for example. This halogen heater is disposed inside of the cored bar of the fixing roller, for example.
On the other hand, a manner (so called IH (Induction Heating) manner) of using an IH coil as a heat source instead of the halogen heater is known. The above-mentioned IH coil generates a magnetic field by way of electrification. Among fixing devices of such IH manner, there exists a fixing device forming the fixing nip by a fixing belt and a pressuring roller instead of forming the fixing nip by a fixing roller and a pressuring roller. The above-mentioned fixing belt is composed of a rotatable endless belt. In addition, an eddy current is generated at the fixing belt byway of action of the magnetic field generated by the IH coil.
Also, as a rotation manner of the fixing belt, a manner of rotating the fixing belt together with one or a plurality of rollers disposed inside of the fixing belt is known. On the other hand, a manner of disposing a pressing member inside of the fixing belt and sliding the fixing belt with respect to the pressing member is known as well.
In the fixing device of such a manner, the fixing belt is prone to deviate to the outside in the direction of a rotation axis of the fixing belt, and one of the important problems is to restrain such deviation of the fixing belt. For example, an end cap is mounted to an end part in the direction of the rotation axis of the fixing belt (hereinafter, simply referred to as an “end part of the fixing belt”), and by the end cap, deviation of a predetermined margin or more of the fixing belt is restrained. In a case where the deviation of the fixing belt is thus restrained by using the end cap, it is desirable to rotate the end cap together with the fixing belt in order to prevent lowering of durability of an end part of the fixing belt. In addition, in order to thus rotate the end cap together with the fixing belt, the end part of the fixing belt may be corrected in a circular shape by the end cap.
A problem in a case where the end part of the fixing belt is corrected in the circular shape by the end cap as mentioned above will be described with reference to FIG. 11.
In a fixing nip 71, a fixing belt 72 comes into pressure contact with a pressuring roller 73, and is pressed by a pressing member (not shown). Thus, the fixing belt 72 is deformed, and a sectional shape of the fixing belt 72 is formed in a shape of an inaccurate circle. In contrast to this, at an end part of the fixing belt 72, a sectional shape of the fixing belt 72 is corrected in a shape of an accurate circle by an end cap 74. Thus, the fixing belt 72 is significantly displaced in a peripheral region of the end part of the fixing nip 71 (refer to the portion Y1 of FIG. 11) and in a peripheral region of the end part of the fixing belt 72 (refer to the portion Y2 of FIG. 11), a stress concentrates on this displaced portion, and there is a concern about damage of the fixing belt 72. In order to eliminate such concern, a distance from the end part of the fixing nip 71 to the end part of the fixing belt 72 is occasionally taken to be sufficiently long (refer to an arrow d of FIG. 11). As a result, a length in a direction of a rotation axis of the fixing belt 72 increases, causing upsizing of a fixing device and eventually leading to upsizing of an image forming apparatus as well.